1. Field of the Invention
The present invention relates to an impact crushing apparatus that mills granular materials, more particularly grain, by impact.
2. Description of the Related Art
A conventional example of a crushing apparatus that mills grain by impact (hereinafter referred to as impact crushing apparatus) is disclosed in International Publication WO 91/11260. Grain is supplied from a supply pipe of the apparatus to a centrifugal wheel, from the outer edge of which the grain strikes against an impact ring due to centrifugal force caused by rotation. The milled grain is ejected from an outlet path. The centrifugal wheel comprises a pair of coaxial rotational disks spaced vertically, one being an inner disk and the other an outer disk, and a plurality of pins, equally spaced in a circumference, connecting the outer edge of the outer rotational disk and the outer edge of the inner rotational disk. These pins disperse blocks of grain moving in the centrifugal direction and evenly direct the grain toward the impact ring. The grain is milled by striking against the impact ring rather than by the pins.
Another conventional example of an impact crushing apparatus is disclosed in Japanese Patent Application Laid-open No. 63-305945. The apparatus is a sample crushing apparatus included in a measuring instrument that analyzes and measures constituents of rice and the like. Granular grain supplied from an opening of the apparatus is impelled toward a perforated ring by centrifugal force caused by rotation of a milling disk, and is beaten and milled between the perforated ring and a plurality of high-speed rotating vanes disposed at the outer edge of the milling disk. The milled grain that has passed through the holes in the perforated ring also passes through a powder collecting path and then is retrieved. The grain is milled repeatedly between the perforated ring and the plurality of high-speed rotating vanes, so it is important to maintain an appropriate clearance between the tip of each vane and the perforated ring for efficient milling. Since these vanes suffer from wear, they must be replaced after being used for a fixed length of time. When the vanes are replaced, however, all vanes must be discarded and new ones must be installed; alternatively, the entire milling disk must be replaced. This is costly and wasteful.
A further conventional example of an impact crushing apparatus is disclosed in Japanese Patent Application Laid-open No. 06-296888. The apparatus crushes pieces of wood by mounting a rotational shaft horizontally in a crushing box and swingably attaching crushing blades to the rotational shaft through supporting plates and supporting shafts. The wood is crushed by the impact of the crushing blades. The crushing blades can be replaced when they wear out. A single crushing blade has a rectangular shape with blade parts at the four corners, prolonging the time during which the crushing blade can be used. However, crushing apparatus of this type cannot be used for milling grain without alteration of its structure.